Telegraph way station selector



sept. i9, 1961 x G. G. LIGHT I'AL TELEGRAPH WAY STATION SELECTOR 15 Sheets-Shea?l 1 Filed Dec. 19, 1957 Sept. 19, 1961 Filed DeC. 19, 1957 G. G. LIGHT ETAL TELEGRAPH WAY STATION SELECTOR FIG.3

15 Sheets-Sheet 2 RSS INVENTORS G. G. LIGHT W. J. WICHTENDAHL ATTORNEY Sept. 19, 1961 G. G. LIGHT ETAL 3,001,009

TELEGRAPH WAY STATION SELECTOR Filed Dec. 19, 1957 l 15 sheets-sheet s FIGA INVENTORS G. G. LIGHT 2 w.J. WICHTENDAHL 27 BY 45 v l uw TELEGRAPH WAY STATION SELECTOR Filed Dec. 19, 1957 l5 Sheets-Sheet 4 IN VEN TORS G. G. LIGHT BY W. J. WICHTENDAHL AT ORNEY Sept. 19, 1961 G. G. LIGHT ETAL TELEGRAPH WAY STATION SELECTOR l5 Sheets-Sheet 5 Filed DeC. 19, 1957 INVENTORS G. GA LIGHT By w. J. WICHTENDAHL AT ORNEY Sept. 19, 1961 G. G. LIGHT. ET AL TELEGRAPH WAY STATION SELECTOR 15 Sheets-Sheet 6 Filed Dec. 19, 1957 --5 T TTUTTQLAOLATELTI I'TLTT m T LTTIN lvuvl Sept. 19, 1961 G. G. LIGHT ETAL TELEGRAPH WAY STATION SELECTOR 15 Sheets-Sheet 7 Filed Dec. 19, 1957 FIG.8

TEXT TxR A INVENTORS G. G. LIGHT BY W. J. WICHTENDAHL RC1-2 i &[ I REPERF.

ORNEY Sept 19, 1961 G. G. LIGHT ETAL TELEGRAPH WAY STATION SELECTOR 15 Sheets-Sheet 8 Filed Dec. 19, 1957 NO ANSWER OPERATE POWER ON DISCONNECT INVENTORS G. G. LIGHT BY W. J. WICHTENDAHL spf. 19, 1961 Filed DSG. 19, 1957 G. G. LIGHT ETAL TELEGRAPH WAY STATION VSELECTOR 15 Shee'b'S-Shet 9 AT ORNEY Sept. 19, 1961 G. G. LIGHT ETAL 3,001,009

TELEGRAPH wAY STATION SELECTOR Filed Dec. 19, 1957 l5 Sheets-Sheet 10 FIG.II

Se TOFIG.|Q

58 INVENTORS Y G, G. LIGHT *To FsGls ATT RNEY BY W. J. WICHTENDAHL Sept. 19, 1961 Filed Deo.

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G. G. LIGHT ET AL TELEGRAPH WAY STATION SELECTOR l5 Sheets-Sheet 1l INVENTORS G. G. LIGHTy w. J. WICHTENDAHL mi few ATT RNEY i Sept. 19, 1961 G. G. LIGHT ETAL 3,001,009

TELEGRAPH WAY STATION SELECTOR Filed Dec. 19, 1957 l5 Sheets-Sheet 12 INVENTORS G. G. LIGHT W.'J. WICHTENDAHL Sept. 19, 1961 G. G. LIGHT ET'AL 3,001,009

TELEGRAPH WAY STATION SELECTOR Filed Deo. 19, 1957 15 Sheets-Sheet 13 `TO FIG.I5

INVENTGRS G. G. LIGHT W. J. WICHTENDAHL fm. Af/1 ATTORNEY Sept. 19, 1961 G. G. LIGHT ETAL 3,001,009v

TELEGRAPH WAY STATION SELECTOR Filed Dec. 19, 1957 TO F|G.I4

TOFIGJ w Mw ATT RNEY Sept' 19, 1951 G. G. LIGHT ETAL 3,001,009

TELEGRAPH WAY STTION SELECTOR Filed Deo. 19, 1957 15 Sheets-Sheet 15 FIG.|6

G. G. LIGHT BY W. J. WICHTENDAHL im @grazw A TORNEY ,aesinet Patented Sept. 19, i951 3,001,009 TELEGRAPH WAY STATION SELECTOR George G. Light, Scarsdale, and William J. Wichtendahl, New York, N .Y., assignors to The Western Union Telegraph Company, New York, N.Y., a corporation o f New York Y Filed Dec. 19, 1957, Ser. No. 703,899

14 Claims. (Cl. 178--2) This invention relates to a Way station selector for a telegraph system and more particularly to a system wherein a central station may select any one of a plurality of way stations for transmission thereto or invite any of the Way stations to transmitto the central station.

The invention is shown with particular reference to a half-duplex telegraph way station system but is equally well applicable to full duplex operation.

The present invention is particularly applicable to a way-wire circuit where it is not feasible to utilize the regular printing telegraph equipment for selecting functions because of non-uniformity of types of apparatus, different signaling speeds, incompatible regenerative repeaters, and the like. Another important reason is that under some circumstances printers might be caused to print spurious characters'in response to a selecting character and this is not tolerable on circuits which handle encrypted messages.

One of the objects of the present system is to provide a way-Wire selector which will operate independently of the regular message transmitter-distributor and printer at the central oice and each of the tributary stations.

A further object is to provide such a station selector which is independent of normal permutation code signals and which will operate solely on timed pulse sequences.

A still further object is to provide such a Way station selector in which each way station is invited to transmit, in turn, so that each station has equal opportunity to transmit to the central station. i

Still another object is to provide a system whereby any way station may request the transmission of a series of invitation cycles by the central station and in which the central station may, in the absence of any such request, initiate such a series of invitation cycles.

Another object is to provide a way-wire station selector in which the central station may select any particular way station to the exclusion of others, for transmission to such selected station and may cut-out such selected station at the end of the period of transmission.

A still further object is to prevent the initiation of Van invitation cycle by the central olice While any Way station is under selection for transmission thereto by the central ofiice.

Other objects and advantages Will hereinafter appear.

The invention will best be understood by reference to the accompanying drawings in which:

FIG. l is a schematic diagram of the central station and way station control circuits;

FIG. 2 illustrates the manner in which FIGS. 3 to 6 and 8 to 16 ofthe drawings are combined;

FIGS. 3 to 6 illustrate the way-station equipment and circuitry;

FIGS. 7A to 7E show the nature and arrangement of the control signals utilized for selecting a way station for reception of a message or inviting a way station to transmit a message; and

FIGS. 8 to 16 illustrate the central-oice equipment and circuitry.

Referring rst to FIG. l, a half duplex system is shown comprising a central station and -a plurality of Way stations, it being assumed in the present embodiment that six such way stations are included Vin the line circuit.

The equipment at the central office includes a receiving relay K-Zl arranged to operate a recorder RC-Z from its marking contact M and having control mechanism associated with its spacing contact S. For simplicity the relay K-ZI is shown operated from a line relay LR differentially connected to the real line L and artificial line AL, although it is to be understood that in actual practice a half-duplex carrier circuit is normally employed. The central otlice is also provided with a plurality of serially connected number transmitters, such as Txr. 1, one for each way station, as will later appear, a text transmitter Txr. A, `and a transmitting relay TR. Battery at the tongue of TR is applied through the make contact of relay TR, the rings of a distributor E-Z or contacts disposed in shunt thereto, and thence differentially to the relay line L and artificial line AL. The line L, at each Way station, is shown connected serially through line contacts, represented by C-6, the contacts of a transmitter 15 and the winding of a line relay K-l, and terminates at ground at the last way station. At each yway station the selecting magnet of a receiving printer 11 is Vconnected from grounded battery through the marking contact of relay K-l to the grounded armature of the relay. An auxiliary ground is also normally applied to the printer magnet by grounding contacts, represented by C-1, so that the printer will not follow the line relay K-I. A clutch magnet 18 is also provided at each way station to effect the operation of the transmitter 15. This magnet is controlled by normally open contacts such as C-2. The manner of selecting a way station for transmission is by closing of clutch contacts (32 at such station and the manner ot selecting the station for reception of a message from the main station is by opening of the printer grounding contact C-1. In a somewhat similar manner, at the central olce the magnet of printer RC-Z is normally grounded by contacts such as C-3 and the operating circuits of the clutch magnets CM-l and CM-A of the numbering machine and text transmitter Txr. 1 and TXr.A are open at contacts C-4 and C-5.

Referring again to the way station, a request button RB is provided at each such station, which the operator may depress whenever he has tape in the transmitter awaiting transmission. The button RB, operating through a group of control relays and timing devices CR-l serves to open the line contact C-6 to send a short open (40 milliseconds) to the central oice. This is known as a request signal and causes the central ofce equip- `ment to send out an invitation cycle composed of a 50,

series of signal sequences, designated as invitation sequences, which invite each of the way stations, in turn,

i to transmit. This request signal busies the control equipment of each of the way stations and at the central oflice acts through line relay K-Zl, a group to control relays CR-2, an invitation relay K-ZS, and a -pulse distributor E2 to set an invitation rotary switch RS-l into operation. The switch RS-l serves to selectively short the transmitting rings of the distributor E-Z, and to control a group of dwell relays DR for transmitting a series of invitation sequences to the `way stations, to thus allow each of the way stations to transmit in turn. On the first invitation sequence should station No. 1 accept the invitation and transmit its message, the following invitation sequence will omit an invitation to station No. 1 and will Erst invite station No. 2. If station No. 2 has nothing to transmit, then station No. 3 will be invited in the same sequence. If station No. 3 accepts the succeediug sequence will start with station No. 4. Sufficient invitation sequences are transmitted to give each station an opportunity to transmit. A second rotary switch RS-Z at the central otice maintains this sequential order central oilice.

of invitation by determining, in each sequence, the first station to which an invitation cycle will be transmitted. Each of the invitation sequences consists of a uniform number of Vopen line conditions which are received on "the line relays K- at each station and serve to voperate gating relays GR 'at each station. The gating relays in tum gate the succeeding pulses to a rotary switch RSS which steps through a complete cycle in making -a station acceptance. The invitation Vsignals each include a llong `dwell or closed line condition following one of such stepping pulses and serve through the control relays CR-1 and associated timing 'devices fof a station, upon accepting the invitation, to lopen the line contacts C-6 to transmit an open condition 'answer-back signal to the l The central cnice, in response to the answer-back signal conditions the printer -ground-at 'C-3 to be opened at the'end of'its invitation sequence toplace the printer Vunder control or the line relay l-21 and also conditions the control relays 'CR-2 `t`o send 'no -further invitation dwells in that invitation sequence but to send stepping pulses only so as to stepeach rotary switch RSS to its home position. Shortly after the switch RSS reaches its home `position the clutch contacts C-Z at the station accepting the invitation, are closed to start the `transmitter 15 into operation. It is assumed that the way stations operate on a torn tape basis and when transmission is completed by tape running out of the transmitter 15, tape contacts 17 open to interrupt the transmi er clutch magnet circuit. A short interval thereafter, the next invitation sequence `is transmitted from the central station and repeated until each station has been invited. The invitation cycle ends with a sequence in which none of the way stations accept the invitation. The function of this last sequence is to restore the way station sets to normal.

VIf no request signals is sent out by any of the -way stations for a prolonged period of time, the central oilice may initiate an invitation cycle. This is effected by a :timer vl31 at thefcentral oice, which operates periodicalwly through the control relays CR-Z, to activate relay K-ZS to initiate such an invitation'cycle.

YShould lthe central oirlce have 4a message `to transmit to any way station it may, by operation of a 'station Aselection key, such 'as S-l, S-2, effect through the control Arelays CR-Z, the operation of selecting relay K-31, which vin turn Vinitiates operation of a stepping switch RS-S 'to Vtransmit a station selection cycle over the lin'e. This cycle will comprise a station selecting sequence and ya station cut-out sequence. The station selection se- :quence 'contains thesame number of spacing pulses as 'each invitation sequence but includes a long dwell which YYonly `follows the stepping pulse corresponding to the station to Vbe selected. The "selected station responds durv'-ing this dwell Vwith an answer-back open line condition which conditions the control relays CR-Z at the central station, so that at the `end -oi the selecting sequence contacts C-i will -be closed to energize the clutch magnet ICM-1 to start the number transmitter Txr. 1 and after Jit has completed its cycle, contacts `C-5 will be closed to energize the clutch magnet CM-A of the text transrnitter Txr. A. The selection signal at Vthe selected 'sta- 'tion alsoacts lto'ope'n the printer ground at contacts C-l -to enable the printer at the selected station to respond 'to the received signals.

At the end of the transmission from the central oiice stepping switch RS-3 resumes its movement to send the station cut-out sequence over the line to restore all of the waystation Vsets to normal.

It is to Abe understood that the disclosure of FIG. l is `fragmentary and -highly schematic and that contacts `such as C-l -to Ce may consist of a number of serial or -parallel arranged relay contacts. The exact nature of `the invitation, selecting and cut-out signal sequences is shown in FIGS. 7A to 7E and these signal sequences will be fullyvdescribed in connection with the detailed station selection.

1 power.

description of the way station circuits of FIGS. 3 to 6 and the central otlice circuits of FIGS. 8 to 16 which follows.

The detail circuits for the control unit at one of the way stations, station No. 2 having been selected by way of example, are shown in FIGS. 3 to 6. Referring now to these figures, the line circuit L (FIG. 6) terminates in the operating winding of the line relay K-l and under idle conditions this circuit is held marking so that the grounded armature of relay K-l is against its marking contact M. This contact is connected directly through the selector magnet 10 of the receiving printer ll to 'battery but the printer is normally held non-'responsive to the line relay by a steady `ground applied thereto over the conductor 12, as will hereinafter appear.

The spacing contact S of the line relay is connected to a circuit A13, -the lfunction iof which is to control, through the receipt of spacing pulses by the relay, the operation of the station selector, either for reception of a message from the central or relay oflice or the transmission of amessage to the central oice.

The line circuit Lis connected from the winding of relay'K-l through the transmitter sending contacts l5 and left armatures and break contacts of relays K-3 and K-4, in parallel.

The selection of a Way station `from the central station is elected through an ll-point 3-level rotary selecting switch RSS (FIG. 3) in which the wiring of levels I and II is identical at all stations, level III being individually coded for each way station. The station 'selecting `points of vlevel III 'arenumbere'd 4 to 9, all but one vof which are strapped together, the unstrapped point being individual to each station. In 'way station 2, of the present example, point 5 is unstrapped and is connected to the tongue a of relay K-lS from which it is extended, as will -be hereinafter described, to eiect the desired The rotary switch has a stepping magnet K-S actuated, as will hereinafter appear, by spacing operations of the line Vrelay K-l under control of a pair of gating relays K-14 and K-l (FIG. 5

When tape to be transmitted from station 2 is placed in the transmitter 16, tape contacts 17 are closed from battery in series with the transmitter clutch magnet 1S,

conductor V19, winding of tape vawaiting relay K-Z and thence by conductor 2i?, and Vtongue b and break contact of relay K-13 to ground. The current in this circuit is suicient vto operate relay K-Z but is not sufficient to operate the clutch magnet 18.

Relay A"Esi-2, when operated, applies 'cattery through tongue b and back contact .of relay i ii and the windingof relay LK-Ztl to the request button RB, the opposite contact of which is grounded.

Assuming power to be on the system relay K-li will normally be operated through the break Contact and tongue fa of relay Ii-S. The application of power also 'cause relay K-7 to operate from battery thro ugh its righthand Writing, over conductor 2l and back contact and tongue c of relay K- to ground. Relay K-7 then locks up to ground at its armature a and causes busy lamp BL to "light over a circuit from ground, lamp 'EL conductor 22, make contact and tongue "b of VVrelay 'Kil to AC. Relay IKJ 'also opens at its tongue Ca request circuit 23, later to be described, which controls theV transmission of a request to -sendsignalsover the line. it also cause operation of relay KLS las follows: rlhe'winding ci K-S is connected from battery through timing tube S-4i to ground. The starting grid of VJ: is connected by armature bof relay K-S and conductor 13 tothe spacing contact S of line relay .K-l, which contact, however,-is open at this time. The :grid isV also connected by conductor 24 toground at Aback 'contact and armature a `of relay K=-7. Upon operation of relay K-7 this ground is Iremoved from the grid of tube V-'4 whereupon the starter anode potential rises under control of the timing condenser and, after an interval of say 3 seconds, tube V-4 tires and relay K-S operates, locking at tongue a and extinguishing the arc in V-4 by the ground applied at this tongue. Ground is also reapplied to the starting electrodes at tongue C. Relay K-S at tongue d closes a previous open in the request circuit 23, referred to above. Relay K-S also 'completes a circuit from the open spacing contact S of the line relay K-1 to the gating relay K-lS over conductor 13, tongue b and front contact of K-S, back contact and tongue b of relay K- and conductor 25 to tongue b and back contact of relay K-15 and thence to the left or operating winding of relay K-14, to power.

During this time the marking contact M of line relay K-l is grounded (l) over circuit 12 at the tongue c of relay K-IZ; (2.) at tongue c of relay 15, and (3) at tongue b of relay K-ll4. As a result no spurious characters may reach the printer 11. Moreover, the clutch magnet 18 of the transmitting-distributor is not energized so that the transmitter can not be operated.

All spacing intervals occurring during normal transmitter-distributor operation and all transmitted station selection or control sequence pulses are substantially less than 3 seconds in duration so that any signals received on the line relay K-l during the 3 second timing interval of tube V-4 would apply ground to the starting anode, at the spacing contact of K-l and thus delay operation of relay K-S until 3 seconds after the arrival of the last space pulse, thus insuring that any control sequence from the central office will have been completed before K-S operates to condition relays K-14 and K-IS to respond to it. This prevents 4the stepping switch RSS from being stepped by a part only of an incomplete control cycle.

Let it be assumed that tape has been inserted in the transmitter 16 and that message waiting relay K-Z is operated in response thereto. If the attendant now depresses the request button RB a circuit is completed to operate the request relay K-Zil from ground at the button to battery at the tongue of relay K-Z. Relay K-20 locks through its armature a and operates the request lamp RL through its armature b.

Thus, with relays K-Z, K4, K-7, K8 and K-20 operated no further action can occur at the tributary station until an invitation sequence is received from the central office. Eventually such an invitation sequence will be received. The transmission of this sequence will be fully described hereinafter with reference FIGS. 8 to 11. For an understanding of the operation of the tributary station control unit, reference is made to FIG. 7A which illustrates the nature of an invitation control sequence effective to select station 2. As will be noted this sequence consists of a busy character (sequence interval a) comprising the code character M having the rest and first two pulses spacing and the last three pulses marking, followed by a two second marking interval or dwell (sequence interval b), an activating character (interval c) which again corresponds to the code character M, followed by two blank or all marking characters or dwells (interval d); two M characters (intervals e and f), to produce two stepping pulses, a two character dwell (interval g), two M characters (intervals h and i) to produce two more stepping pulses, a second two second dwell (interval j), another M character (interval k) to produce another stepping pulse, a third two second dwell (interval l) and a group of `six M characters (intervals m to r) to produce a group of six stepping pulses.

When the first activating or busying character comprising sequence interval a is received, the line relay K-I goes to its spacing contact, thus applying ground through armature b of operated relay K-S, armature b of unoperated relay K-10, conductor 25, and armature b of unoperated relay K-lS, to the left Winding of relay K-14, thereby to operate this relay at all tributary stations. At tongue b relay K-14 applies ground over a circuit including` the conductor 26, back contact and tongue d of relay K-9, and thence through the right winding of relay K-10, which operates and locks atits tongue a and sets up its own delayed release circuit by removal of ground at tongue c from the grid of timing tube V-S, the anode `circuit of which is connected to battery through made armature and the left winding of relay K-ltl in opposition to its right hand winding.

Relay K-ltl, at its tongue b disconnects the grounded space contact of line relay K-l from relay K-14, causing relay `KelS to operate by current ow through the left winding of 1914, its tongue c, and right winding of relay K15, to ground at tongue e of relay K-lfl, whereby these relays lock together.

Relay K-9 is also operated through its left Winding to ground rat tongue c of relay K-ltl. It thereupon (l) locks up at its tongue c and (2) operates busy lamp BL (if not already operated by relay K-7) over a circuit shunting tongue b and make contact of relay K-' and including tongue b and make contact of relay K-9. Relay K-9 also (3) sets up its own knock-down circuit from its right winding and tongue a and conductor 27 to point 10 of level HI of the rotary switch RSS and (4) transfers, at tongue d, operative control of relay K-lll) from tongue b of relay K-14 to conductor 28 and the strapped points 4 to 9 of level Il of the rotary switch. In addition relay K-9 (5) at its armature e opens the request circuit 23e at each tributary station, so as t-o prevent any request to send being made by any of the other tributary stations, as will more fully appear hereinafter.

Early in the two second dwell (sequence interval b) following the busying pulse, relay K-ll and K-lS are knocked down as described below and towards the end of this dwell relay K-10 is knocked down by firing of its timing tube V5. Relay K-9, however, remains operated. Relay K-14 is released by timing tube V-1, the anode of which is connected through armature a and the right 'winding of the relay in opposition to the left winding, the normal ground of the starting anode of V-l being lifted at tongue f of relay K-14 and tongue g of relay K-l, when both relays are operated. Following release of relay K-14 relay K-15 is released by removal of ground from the starting electrode of the timing tube V- at armature f land make Contact of relay K-14. When tube V-6 res a circuit is completed from battery at break contact and tongue e of relay K-ll4, right winding of relay K-lS, in opposition to its left holding winding, make contact and tongue a of K-15, conductor 29, tongue c and break contact of relay K-19 and conductor 30, to the anode of tube V-6, the cathode of which is grounded.

Thus with relays K-10, K-14 and K-lS released during interval b, the second space pulse or activating character (sequence interval c) again operates relays K-14 as before, relay K-l however remaining unoperated since its control was transferred from relay K-14 to the rotary switch RSS; but at the end of this spacing pulse, when ground is removed by the line relay K-l from the outer terminal of the left hand winding of relay K-ll4, the current through this winding is again extended through the right winding'of relay K-lS to operate the same and causing it to lock-up with relay K14 as before.

During the following dwell (interval d) the tube V-l operates to again release relay K-14. This two character length dwell, which at normal signaling speeds is about 0.4 seconds in duration7 is not sucient for tube V-6 to fire following the release of relay K--lland therefore K-15 remains energized. With relay K-14l released and K-15 operated a circuit is extended from spacing contact S of line relay K-1 over conductor 13, tongue b and make contact of relay K-S, back contact and tongue b of relay K-lll, conductor 2S, `tongue b and make contact of K-15, armature d and back contact of relay K-ld, conductor 31, through the winding of a relay K18 and thence to the stepping magnet K-S of switch RSS to battery. The stepping magnet K-S is designed to step on release. Relay K-1S is slow-to-release, holding for 200 or more milliseconds after its circuit is opened. An associated relay l-16 is operated and released directly in response to the operation and release of relay K-18 but is slow to the extent that its release follows that of relay i918 by about 40 milliseconds.

Now, with relay K-l4 released and relay K-l' operated, upon the reception of the spacing pulse (interval e of the control sequence), ground is applied over the circuit last traced to energize the slow-to-release relay K-l and step magnet K-S, relay .l-16 operating from the contacts of K-l. The following marking pulse of interval e releases the .step magnet K-S which steps its wiper from the llth or home position shown to its point 1. Since this marking pulse is only about 100 milliseconds in length, relay K-l8, with its 200 millisecond release period, holds operated.

At level 1 of the rotary switch the wiper W-l applies ground by conductor 32 to the winding of relay K-l, which operates and loc-ks through its tongue a, and conductor 33 to `ground at tongue g of relay K-l. Relay K-19 prevents release of K-lS (which is locked through its armature f) by applying ground at armature b and conductor 34 to the starting anode of timing tube V-6 and, at armature c, removing the anode of tube V-6 from connection with 'the right winding of K-15 No connections are established at levels II or III of the rotary switch on this first step. The next spacing pulse (sequence interval f) steps the switch RSS to point 2 and the long dwell which follows (interval g) permits relays K-lffl to release and relay lli-16 to release 40 milliseconds later. During this 40 millisecond interval ground is applied from armature b of released relay K-Il, and armature b of operated relay K-lo to the wiper of level HI of switch RSS, and thence from point 2 thereof over conductor 35, armature a and back Contact of relay K-ll and conductor 36 to the right winding of relay K-7, to operate this relay, if not already operated.

The next two space pulses (sequence intervals h and i) step the rotary switch to point 4, and the two second dwell (interval j) again connects ground to wiper Ill for 40 milliseconds. This point 4 is the identifying point on the rotary switch for tributary station No. l and if this station has nothing to transmit no action results.

The next space pulse (interval k) and the following dwell steps the switch to point this being the identifying point for station No. 2, which it has been assumed has tape in its transmitter l5 and has had its request button RB depressed to operate relay K-2ll. When ground is now applied to wiper IH during the milliseeond interval following release of relay K-l8, this ground is applied frorn point 5, at station No. 2, through tongue a and back contact of relay K-l3, conductor 37, make contact and tongue c of relay K-Zl to the left winding of station selection relay K-l, causing this relay to operate and lock-up at armature f.

Operation of relay K-1l (l) lights the send lamp SL from ground at the lamp and tongue e of relay K-l1 to A.C. power. It also (2) releases relay K-Zt at its tongue b thus extinguishing the request lamp RL, and (3) prepares its own knockdown circuit through timing tube V-3 by applying ground 4to the cathode of the tube through its tongue c and malte contact, and tongue d and break contact of relay 'l-6, thus conditioning V-3 to operate after a 20 second delay. In addition relay lli-11 (4) closes ground to the cathode of timing tube V7 over conductor 3S, tongue e land rear contact of relay K-lS, and thence by conductor 39 through the malte contact and tongue g of relay K-ll to ground; (S) extends an operatingcircuit for relay K-6- from battery at the tongue of relay KfZ, tongue b and make contact of relay K11 to the winding-of relay `K6 and to the anode of timing tube V-Z, the cathode of which is connected through armature d and make contact of relay K-ll, conductor 40, armature e and make contact 'off relay K-IS 8 and thence by conductor 41 to 'B battery 'at 'the starting electrode of timing tube `V-2. This tube tires shortly after the rotary switch moves to its home position to operate relay K-6 as willrlater appear.

The above mentioned application of ground to tube V-`7 causes this tube -to lire in the early portion of the two second dwell (interval L) thereby operating relay K-3, connected in the tube circuit. lopens the line circuit L at armature c and the circuit of relay K-d at armature a. Relay K-4, as stated, is timed to release 40 milliseconds later, thus again closing the line circuit at its armature. The 40 millisecond open is thus sent to the line and serves as au answer-back to the central office that -a message is to be picked up at tributary station No. 2s. This answer back signal (indicated in dotted line in FG. 7A, interval L) actuates means at the central station, as will be fully described hereinafter, to alter the invitation sequence being transmitted by omitting all further two second dwells after the stepping pulses so that the following intervals m to r comprise stepping pulses only.

During the foregoing movement of switch RSS, upon the stepping of this switch to its fourth point and during the 40 millisecond release period of relay ir-16 following release of relay Ki, a pulse is sent from ground at relay K-l through armature a of relay K-l, Wiper W-Z or" level Hand point l thereof, conductor 2S, make contact and tongue d of relay K-9, to the operating winding or relay K-ltl, causing this relay to operate and at its tongue b -to .interrupt the circuit to the spacing contact of line relay K-l. The purpose of this is to disconnect the line relay from the stepping magnet of switch RSS at each way station during the 40 millisecond answer-back Signal which -would have been sent over the line had station l been selected and thus prevent false stepping of the rotary switch. Relay K-ll is self-timing as previously described and releases prior to the next stepping pulse (interval It) and operates again for a similar purpose during the following dwell (interval'L) when station No. 2 is selected and transmits .its '40 millisecond answer-back signal. About the middle of this dwell relay Kel@ again releases.

Following dwell L the central ollice, as stated, transmits a series of stepping pulses without intermediate dwells. Since relay K-l does not releasebetween such pulses no further circuits are completed through the ro tary switch until the brushes reach point ill whereupon Wiper W-l connects ground through made tongue c of relay K-19, conductor 29, made tongue a of relay K-Il5, its right winding in opposition to the left winding thereof(` and to battery at tongue e and back contact of relay K-14. Consequently relay K-S falls down and interrupts the locking circuit of relay K-l@ so that it releases. Relay K-15 connects ground to the cathode of timing tube V-2 from back contact and armature@ of this relay, conductor 40, and made armature d of relay K-ll.. A short period later tube V-2 lires causing relay K- to operate and lock at its tongue a. The operation of relay K-6 shunts relay K-2 over made tongue c of K--d without, however, releasing relay K-Z, and thus allows current to -rise in the transmitter-distributor clutch magnet i8 to a level suiicient to start the transmitter and cause the message in its tape to be transmitted. The tlrst character sent will activate the receiving relay lto spacing at all tributary stations to operate relays K-M and K-lS. Since no long dwells occur during .normal tape transmission, relays K-14 and K-S remain operated until the end of the message. With both of these gating relays operated the rotary switch stepping circuit is held' open so that false stepping of the switch cannot occur.

At the completion of the message, as the ltape runs out of the transmitter, contact 17 opens, releasing relay K-Z and thus releasing relay K-5.

VDuring transmission from station No. 2, the intermittent ground applied to the starting electrode of tube V- at the spacing Contact S of relay K4 'prevents this tube from tiring. However, affraction yof a second after fthe tape runs eut, tube V-i will fire to knock down relay I l-l4- This applies battery from tongue e of relay K-14, through the right winding of relay K-IS, its tongue a, conductor 29, tongue c and back contact of relay K-19, and conductor 3l), to the anode of tube V6, and also removes ground from the starting electrode of tube V- at tongue f of relay K-14. Shortly thereafter tube V-6 conducts and knocks down relay K-15. The release of relay K- applied ground to the cathode of the 20 second delay tube V-3 at armature d and back contact of relay Ken, and made tongue c of relay K-ll and therefore tube t-3 res 20 seconds after the end of the message, knocking down relay K-lll through its opposed right winding.

Relay K-lll on its release opens, at its tongue g the initiate circuit of the answer-back signal, including the conductors 33, 39 and tube V-'7 so that relay K3 releases. Relay K-4 is then reoperated from tongue of relay K-S so that the sending loop 14 is held closed by one or the other of these relays at all times. The circuits at all tributary stations are now returned to normal idle condition with relays K-4, K-7 and K-S operated.

Within a prescribed period after the end of the message the central oice will start another invitation sequence similar to the one described except that no dwells will be inserted after the fourth and fifth stepping pulses (stations Nos. 1 and 2 selections) so that the rst station which may respond will be station No. 3 and if this or any higher numbered station have requests waiting the message is accepted from the next higher numbered station. Thereafter new inviting sequences will be transmitted until all stations have had an opportunity to transmit.

Station No. 6 is the last stationafforded an opportunity to transmit. If this station accepts the invitation, transmission will proceed therefrom in the same manner as described with reference to station No. 2. Following this transmission the central office will transmit a iinal signal sequence, of the form shown in FTG. 7B, in which no invitation dwells are included but in which a two second dwell is inserted at the end of the tenth step pulse, the purpose or" which is to restore the tributary station relays to their normal condition. However, if station No. 6 fails to respond during the invitation dwell provided for it after the ninth step pulse, then the absence of an answer-back or acceptance signal during such invitation dwell period will be sensed at the central office and the station normalizing two second dwells will be inserted after the next or tenth step pulse of this same signal sequence. This dwell will occur with all of the rotary switches on point 10 and during this dwell a 4() millisecond pulse will be sent from ground at relay K-18, wiper W-3 and point it) of level III, conductor Z7 and tongue d and make contact of relay K-7 to the left or opposing winding thereof, thereby knocking down all relays K-7. A parallel circuit, through tongue a and right winding of relay K-9, also releases relay K-9 at each station. The final stepping pulse steps the rotary switch to its home or point 11 position. `ln the dwell following the eleventh stepping pulse ground from wiper W-1 and point l1 of level I causes relays K-llS and K-19 to be released at all stations, as previously described, to restore all station sets to the normal idle status with relays K-4 and K-S only operated.

It will be remembered when power was rst applied to the station sets, that relays K-4, K-7 and K-S were operated and that transmission from station No. 2, for example, could only result in response to an invitation sequence from the central oiiice. However, after the final sequence, with -relay K-7 released, it is possible for any station to transmit a request to transmit to the central othce. rlhus with tape in the transmitter and relay K-Z operated as a consequence thereof, the depression of request button RB operates relay K`20 as before described. With relay K-' now released a ground for the cathode of timing tube V-7 is applied by a circuit extending from the cathode, over conductor 3S, tongue e and back con"-I tact of relay K-13, conductor 39, make contact and tongue d of relay K-Zt), conductor 42, back contact and tongue c of relay K-7, make contact and tongue d of relay K-S, back contact and tongue e of relay K-9, conductor 23, back contact and tongue d of relay K15, conductor 43 and back contact and tongue b of relay K-lZ to ground. Thus tube V-7 res and operates relay K-3, opening the sending circuit, and 4() milliseconds thereafter relay K-4 operates to reclose the sending circuit. This 40 millisecond open serves the same purpose at all other tributary stations as the busy signal (interval a of FIG. 7A) previously discussed. The response of the central oce to this request signal is, following a two second dwell, to transmit an activating character followed by the ll stepping pulses and appropriate dwells to effect a selection of the station making the request. The manner in which the central oce reacts in response to this request will be described with reference to FIGS. 8 to 16.

It will be noted then that the selecting equipment at each tributary station will respond to invitationy signals either sent periodically by the central oflice or sent in response to a request transmitted by the tributary oice. In addition the station sets may be selected by the central ofiice for the reception of messages from the central oiice. This selection of a particular tributary station will now be described.

Assuming the central oce has a message to transmit to tributary station No. Z, it will first send a selection sequence of the form shown in FIG. 7C. FIG. 7D shows the the sequence which would serve to select station No. 6. At the time the selecting signals (FIG. 7C) are transmitted by the central oice it is to be remembered that relays K-4 and K-S will be operated at the tributary stations.

In response to the iirst spacing or busying character the line relay K-l applies ground through previously described contacts of relays K-S, K-10 and K-1S to operate relay K14. The latter operates relay K-lt), which sets up its own knockdown circuit through tube V-S, operates K-9 and opens the circuit extending from the spacing contact of line relay K-1, thus electing operation of relay K-14, all as previously described with reference to the busying pulse of an invitation sequence. Relay K.9 opens the circuit of request control tube V-7 so that no request may be transmitted from any of the tributary stations during the remainder of the selecting sequence. During the two second dwell following the busying impulse tube V-l under control of the operation of relay K-lS lires and knocks down relay K-14 which in turn activates tube V-6 to knock down relay K-15. Relay K-lltl also releases under control of its timing tube V-S, leaving at the end of the first two second dwell relays K-4, K-8 and K-9 in operated condition.

The activating character again operates relays K-14 and K-15. Relay K-l() does not operate in this cycle since its circuit is made through the back contact of now operated relay K-9. During the following two character dwell K-14 is again knocked down by its timing tube but relay K-15 remains operated due to the shortened period of this dwell (approximately 0.4 second). Thus at they end of the dwell following the activating pulse relays K-4, K-8, K9 and K-lS are operated and the spacing contact of the line relay is extended through contacts of relays K-10, K-S, K-14 and K-IS to the winding of relay K-lS and stepping magnet K-5.

The next pulse (1st step pulse) operates relay K-lS which operates relay K-16, as before described, and at the end of the pulse the rotary switch steps from point 11 to point 1. At level I point 1, the wiper W-l grounds relay K-19 which on operating holds gating relays K-ll'4 and K-lS in their respective unoperated and operated conditions. During the following two character dwell a 40 millisecond ground is applied by relays K-l8 and K-l over wiper W4 and point l of level HI to operate :relay 

